DGTREAL Discrete Gabor transform for real-valued signals
Usage: c=dgtreal(f,g,a,M);
c=dgtreal(f,g,a,M,L);
[c,Ls]=dgtreal(f,g,a,M);
[c,Ls]=dgtreal(f,g,a,M,L);
Input parameters:
f : Input data
g : Window function.
a : Length of time shift.
M : Number of modulations.
L : Length of transform to do.
Output parameters:
c : M*N array of coefficients.
Ls : Length of input signal.
DGTREAL(f,g,a,M) computes the Gabor coefficients (also known as a
windowed Fourier transform) of the real-valued input signal f with
respect to the real-valued window g and parameters a and M. The
output is a vector/matrix in a rectangular layout.
As opposed to DGT only the coefficients of the positive frequencies
of the output are returned. DGTREAL will refuse to work for complex
valued input signals.
The length of the transform will be the smallest multiple of a and M*
that is larger than the signal. f will be zero-extended to the length of
the transform. If f is a matrix, the transformation is applied to each
column. The length of the transform done can be obtained by
L=size(c,2)*a.
The window g may be a vector of numerical values, a text string or a
cell array. See the help of GABWIN for more details.
DGTREAL(f,g,a,M,L) computes the Gabor coefficients as above, but does
a transform of length L. f will be cut or zero-extended to length L before
the transform is done.
[c,Ls]=DGTREAL(f,g,a,M) or [c,Ls]=DGTREAL(f,g,a,M,L) additionally
returns the length of the input signal f. This is handy for
reconstruction:
[c,Ls]=dgtreal(f,g,a,M);
fr=idgtreal(c,gd,a,M,Ls);
will reconstruct the signal f no matter what the length of f is, provided
that gd is a dual window of g.
[c,Ls,g]=DGTREAL(...) additionally outputs the window used in the
transform. This is useful if the window was generated from a description
in a string or cell array.
See the help on DGT for the definition of the discrete Gabor
transform. This routine will return the coefficients for channel
frequencies from 0 to floor(M/2).
DGTREAL takes the following flags at the end of the line of input
arguments:
'freqinv' Compute a DGTREAL using a frequency-invariant phase. This
is the default convention described in the help for DGT.
'timeinv' Compute a DGTREAL using a time-invariant phase. This
convention is typically used in filter bank algorithms.
DGTREAL can be used to manually compute a spectrogram, if you
want full control over the parameters and want to capture the output
:
f=greasy; % Input test signal
fs=16000; % The sampling rate of this particular test signal
a=10; % Downsampling factor in time
M=200; % Total number of channels, only 101 will be computed
% Compute the coefficients using a 20 ms long Hann window
c=dgtreal(f,{'hann',0.02*fs'},a,M);
% Visualize the coefficients as a spectrogram
dynrange=90; % 90 dB dynamical range for the plotting
plotdgtreal(c,a,M,fs,dynrange);
References:
K. Groechenig. Foundations of Time-Frequency Analysis. Birkhauser, 2001.
H. G. Feichtinger and T. Strohmer, editors. Gabor Analysis and
Algorithms. Birkhauser, Boston, 1998.
Url: http://ltfat.github.io/doc/gabor/dgtreal.html
See also: dgt, idgtreal, gabwin, dwilt, gabtight, plotdgtreal.
Package: ltfat